1. Field of the Invention
The present invention relates to circular polarizers and liquid crystal displays provided with the same.
2. Background Information
In recent years, liquid crystal displays have been expected to become increasingly used in the field of displays for personal digital assistants (PDA), for example, where their thin and lightweight characteristics can be fully exploited. Since such personal digital assistants (PDA) are generally driven with batteries, it has been necessary to keep the electricity to be consumed by them as low as possible. Therefore, attention has been drawn particularly to reflective type liquid crystal displays for the personal digital assistants which are free of or need not use at all times an electricity-consuming back light and can be reduced in electricity consumption, thickness, and weight.
There have been widely used reflective type liquid crystal displays with two polarizers for black-and-white display in which a liquid crystal cell is sandwiched between a pair of polarizers and a reflector is disposed the outside of one of the polarizers. Furthermore, recently a reflective type liquid crystal display with a single polarizer in which a liquid crystal layer is sandwiched between a polarizer and a reflector has been proposed and practically used because it is brighter in principle than those with two polarizers and is easy to be colored as reported in JAPAN DISPLAY, 192 (1989) by T. Sonehara et al. However, these reflective type liquid crystal displays have a drawback that the displayed images become invisible when they are used in a dark place because they usually display the images using light from the outside of the displays.
To solve this problem, there has been proposed a transflective liquid crystal display with a single polarizer in which a transflector is used to transmit part of an incident light instead of the reflector, and a back light is provided, as described in Japanese Patent laid Open Publication No. 10-206846. Therefore, this display can be used as a reflective type, i.e., in a reflection mode using light from the outside when the back light is not turned on and as a transmission type, i.e., in a transmission mode using the back light under dark situations.
The transflective liquid crystal display with a single polarizer needs to make substantially circularly polarized light incident on the liquid crystal cell through the transflector in the transmission mode. Therefore, it is necessary to dispose a circular polarizer comprising one or more polymeric stretched films typically formed of polycarbonates and a polarizer between the transflector and the back light. However, in the transmission mode of a TN-LCD, there is a problem relating to viewing angle in that the displayed images are changed in color and decreased in contrast when viewed obliquely, due to the birefringence peculiar to the liquid crystal molecules and it is essentially difficult to enlarge the viewing angle with a circular polarizer having polymeric stretched films.